1. Field of the Invention
The present invention relates to an image reading apparatus which irradiates a light to a light transmissive document sheet such as a film held on a slide mount to read an image.
2. Related Background Art
In the past, a film scanner which has a function of automatic frame feed to automatically feed films sequentially one by one into an illumination unit has been widely known. This apparatus generally comprises a tray for accommodating films which are a light transmissive document sheets held on slide mounts, an illumination unit provided at the bottom of the tray, and a CCD line sensor for reading an image of the film fed into the illumination unit.
The films separately accommodated in the tray are sequentially fed into the illumination unit one by one upon depression of a drive button by an operator and the film is irradiated by a light from a light source such as a halogen lamp provided in the illumination unit. The light image is projected to a read unit so that the image is read by the CCD line sensor.
Each time the drive button is depressed for a short period, the tray is driven by one frame and the film in the accommodation unit corresponding to that frame is fed into the illumination unit. When the drive button is depressed continuously for a long period, the film is automatically and sequentially fed into the illumination unit one by one by an automatic frame feed function so that continuous image read is attained.
A film scanner having an optical viewer has also been widely known. In this apparatus, after a light has been irradiated to a film in the illumination unit, a light image thereof is projected to a screen of the optical viewer so that an operator may search the images of films while he/she watches the projected images.
An automatic focusing mechanism for precisely focusing an image light transmitted through a film onto a CCD line sensor has also been proposed. However, when the focus of the projection lens for focusing the image light from the film onto the CCD line sensor or the optical viewer is adjusted for the automatic focusing, a projection magnification of the image may change before and after the focus adjustment.
If the change of the projection magnification is large, the image cannot be read with a proper magnification and the image may be read with an edge thereof dropped.
It is also proposed to overlay a trimming frame on an optical viewer to indicate trimming. In this apparatus, a light transmissive liquid crystal display panel and a screen are built in the optical viewer and an document sheet image is projected from a rear side to the screen built in the optical viewer. In a trimming mode, the position and the size of the trimming frame displayed on the light transmissive liquid crystal display panel are controlled through console keys to determine a trimming area. When the start of the reading of the image is instructed, the automatic focusing and the automatic exposing are conducted and then the reading of the image is started.
In the prior art apparatus, however, since the automatic focusing is effected after the definition of the trimming area, the projection magnification onto the image pickup elements may change to a different one than that instructed for the trimming area and the trimming area may be shifted before and after the automatic focusing. In order to avoid the change in the magnification, the trimming may be effected after the operator has effected the automatic focusing operation, but this makes the operation complicated.
Further, when the automatic focusing is effected immediately after the mounting of the document sheet, the image may not immediately appear on the display.